How Machine Guns Work

In the last section, we saw that a cartridge consists of a primer, a propellant and a projectile, all in one metal package. This simple device is the foundation of most modern firearms. To see how this works, let's look at a standard double-action revolver.

Keep Reading Below

This gun has a revolving cylinder, with six breeches for six cartridges. When you pull the trigger on a revolver, several things happen:

Initially, the trigger lever pushes the hammer backward. As it moves backward, the hammer compresses a metal spring in the gun stock (the handle). At the same time, the trigger rotates the cylinder so the next breech chamber is positioned in front of the gun barrel.

When you pull the trigger all the way back, the lever releases the hammer.

The compressed spring drives the hammer forward.

The hammer slams into the primer at the back of the cartridge, igniting the primer.

The primer sets off the propellant.

The exploding propellant drives the bullet out of the gun at high speed.

The inside of the barrel has a spiral groove cut into it, which helps spin the bullet as it exits the gun. This gives the bullet better stability as it flies through the air and increases its accuracy.

When the propellant explodes, the cartridge case expands. The case temporarily seals the breech, so all the expanding gas pushes forward rather than backward.

Obviously, this sort of gun is easier to use than a flintlock or a percussion cap weapon. You can load six shots at a time and you only have to pull the trigger to fire. But you're still fairly limited: You have to pull the trigger for every shot, and you need to reload after six shots (although some modern revolvers can hold 10 rounds of ammunition). You also have to eject the empty shells from the cylinders manually.

Now let's take a look at how gun manufacturers addressed the disadvantages of using revolvers.